The objective of this research proposal is to use SV40 as a simple model to study the basic mechanism of gene regulation of mammalian cells. We plan to: 1. Analyze the mechanism for the production of SV40 mRNA by studying the relationship among various post-transcriptional processing steps for the generation of mature mRNA. 2. Analyze the regulation of SV40 late gene expression during early or abortive infection by analyzing the rate of late mRNA synthesis and its subsequent processing. 3. Analyze the secondary structure of SV40 late nuclear RNA cross-linked in vivo in the search of structural basis for splicing.